Field issue regarding construction of straight shaft drilled pier

[oengineer]

I received a question from the construction team of a project I am working on. It is a structural field issue.

In the course of drilling a straight shaft pier for a building, the cage caught on the casing as it was being pulled out of the hole. The construction team was advised to fill in the hole. The pier hole was cleaned out and all concrete was removed. Then the hole was filled back in with dirt.

I am open to suggestions and recommendations on how to proceed.

 

[JAE]

If the pier depends on skin friction then I'd re-drill a slightly larger hole to ensure adequate and competent surrounding earth.
I might also deepen it a bit to also ensure adequate capacity.

If it is end-bearing only - I'd just have them drill a bit deeper with the same diameter.

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[BridgeSmith]

If the shaft is to carry the axial load in end bearing, then the solution seems fairly straightforward - just redrill a little deeper, and more on.

If it's supposed to carry the axial load in skin friction along the sides, or if it's carrying lateral load, then the condition of the borehole wall becomes important. When the casing was withdrawn and the concrete removed, did the wall cave in badly? If so, the only viable option may be to redrill without the casing, so that there's concrete interfacing with undisturbed soil. It will obviously use a larger volume of concrete, but having loose soil around the shaft compromises both the friction and lateral bearing capacity.

Edit: I see you beat me to the punch, JAE.

 

[oengineer]

@JAE and HotRod10 :

Thank you both for your responses!

 

[JAE]

HotRod10 - Great minds think alike!

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[BridgeSmith]

...and so do we, apparently.